1. Field of Invention
The present invention relates to a fuel supply apparatus for a Gasoline Direct Injection (GDI) engine, and particularly to a fuel supply apparatus for a GDI engine having reduced pressure pulsation which makes it possible to reduce pressure pulsation occurring in a high pressure fuel pump with the aid of a low pressure fuel pump of a fuel supply apparatus of a GDI engine which operates with a variable fuel pressure.
2. Description of Related Art
In a Gasoline Direct Injection (GDI) engine, when a low pressure fuel pump installed in a fuel tank supplies fuel to a high pressure fuel pump installed in an engine, the high pressure fuel pump pressurizes the fuel, and the pressurized fuel is sprayed from an injector of a cylinder.
Referring to FIG. 1, an example of a conventional fuel supply apparatus for a GDI engine will be described. The conventional fuel supply apparatus for a GDI engine includes a low pressure fuel pump 21 which is installed at one side of a fuel tank 10 and works with a fixed fuel pressure, and a high pressure fuel pump 31 which is mounted on an engine and supplies a high pressure fuel to the injector. On a fuel supply line 40 connecting both the low pressure fuel pump 21 and the high pressure fuel pump 31 is installed a regulator 41 which is configured to return fuel to the fuel tank 10. With the above mentioned construction, the fuel supplied from the low pressure fuel pump 21 except for the fuel which is sprayed to the injector via the high pressure fuel pump 31 is returned to the fuel tank 10 via the regulator 41.
In addition, at the low pressure fuel pump 21 is disposed a check valve 21a for the purpose of preventing the fuel supplied from the low pressure fuel pump 21 to the fuel supply line 40 from flowing in a reverse direction. At one side of the fuel tank 10 is disposed a suction jet pump 12. The fuel residing at the other side of the fuel tank 10 to be transferred as part of the fuel discharged from the low pressure fuel pump 21 forms a negative pressure while it is passing through an orifice. And at the other side of the fuel tank 10 is disposed a suction sub filter 11 for the purpose of filtering impurities contained in the fuel which is supplied to the suction jet pump 12.
The regulator 41 is installed at a downstream of the low pressure fuel tank 21 which discharges fuel with a fixed fuel pressure and is configured to open when a pressure pulsation exceeds a previously set discharge fuel pressure of the low pressure fuel pump 21.
When the pressure pulsation occurring in the high pressure fuel pump 31 is transferred to the low pressure fuel pump 21 along the fuel supply line 40, the regulator 41 opens and enables the fuel to return to the fuel tank 10 thereby eliminating pressure pulsation.
As shown in FIG. 2, a system is disclosed recently, which is configured to enable a low pressure fuel pump 21 to discharge fuel with a variable fuel pressure depending on the fuel pressure which is variably determined by the ECU (Electronic Control Unit) 51 based on the operation condition of an engine.
A relief valve 42 is installed on the fuel supply line 40 connecting both the low pressure fuel pump 21 installed in the fuel tank 10 and the high pressure fuel pump 31 installed at the engine 30, and a pressure sensor 43 is installed between the low pressure fuel pump 21 and the relief valve 42. The fuel pressure measured by the pressure sensor 43 is outputted to the ECU 51, and the ECU 51 is configured to set a target fuel pressure and to control the low pressure fuel pump 21 by way of a fuel pump controller 52. The relief valve 42 opens and allows fuel to bypass only when the pressure level of the fuel supply line 40 is over a preset pressure under the abnormal situations that a pressure pulsation occurs in the high pressure fuel pump 31 or a filter is blocked.
In the above described construction, since the relief valve 42 remains being closed when the pressure pulsation occurring in the high pressure fuel pump 31 is below the operation pressure of the relief valve 42, it is impossible to eliminate a pressure pulsation.
Since the pressure pulsation is not eliminated, the pressure sensor 43 disposed between the relief valve 42 and the high pressure fuel pump 31 on the fuel supply line 40 could continue computing inaccurate values. In other words, when pulsation occurs due to the pressure in the high pressure pump 31, the pressure sensor 43 computes or measures, as pressure value of the fuel supply line 40, the duplicated values of the fuel pressure of the low pressure fuel pump 21 and the pressure pulsation transferred from the high pressure fuel pump 31, and thus the inaccurately measured pressure values are transferred to the ECU 51. The ECU 51 transfers the target fuel pressure determined from the inaccurate values to the controller 52, and the controller 52 comes to control the operations of the low pressure fuel pump 21 so that an incorrectly determined target fuel pressure is obtained.
As the pressure pulsation of the fuel supply line 40 is continuously measured by means of the pressure sensor 43, the fuel pressure keeps varying, so there will be a large difference between the target fuel pressure and the actual fuel pressure. As pulsation increases in the actual fuel pressure, the fuel pressure feedback control of the fuel pump controller 52 becomes defective.
In addition, as the pressure pulsation increases in the fuel supply line 40, pulsation sounds are generated, and the feedback control of the fuel pressure becomes poor, so engine operation problems such as a defective engine start, an engine stop, a non-uniform engine operation occur in the conventional art.
The information disclosed in this Background section is only for enhancement of understanding of the general background of the invention and should not be taken as an acknowledgement or any form of suggestion that this information forms the prior art already known to a person skilled in the art.